A 21+

  • A 21+
A 21+ A 21+ A 21+ A 21+ A 21+ A 21+ A 21+ A 21+ A 21+


A 21+



Parasound’s big bruiser of a muscular yet always adept power amplifier gets a powerful update with a new "Plus Series" model. The Halo A 21+ improves on the already over-the-top amazing Halo A 21 via carefully thought-out performance upgrades for cleaner, ultra-low distortion sound, revised front panel cosmetics, and a revised rear panel layout offering enhanced features, too. More than ever, this beefy Parasound amp is an elegant brute, able to effortlessly deliver crashing crescendos in all their incendiary glory while also adroitly turning on a dime to reproduce ever nuance of a quietly quivering violin string.

The March 2020 issue of Stereophile magazine features a rave review by Kalman Rubinson, who says, "Listening to the A 21+ was eminently delightful and satisfying from the first note." According to Rubinson, "Over a span of weeks, the A 21+ was a constant companion and a bringer of musical enjoyment; compared with other amps on hand and in spite of a few sonic differences, the new Parasound was impossible to fault."

Rubinson concludes, "Anyone in the market for a stereo power amp would be well advised to consider the Parasound A 21+, especially those who believe they must spend more. With apologies to W.S. Gilbert, it is the very model of a modern power amplifier."

Specifications and Features:

A21+ Performance Upgrades

  • Power up 25-30%
  • Filter capacitance up 20-30%
  • 10-15% Larger main power transformer
  • Upgraded internal gold on gold audio connections (cleaner signal path and more reliable)
  • Tweaked input circuits for Improved Crosstalk specs
  • Improved power supply for lower distortion at full power
  • Filter capacitance: 108,000 uF
  • Transformer size: 1.3 kVA

Revised Halo Front Panel Cosmetics

  • Slim metal end caps replace wider plastic end caps
  • Added gold metallic accent stripe along end cap
  • Engraved metal PARASOUND badge replaces the red P
  • Gold feet now on black units

Revised Rear Panel Layout and Features

  • Upgraded speaker terminals (A21+ gets JC5 terminals)
  • New jack/terminal layout with more space and more clear text/labels
  • 2.5mm trigger jacks replaced with 3.5mm jacks
  • Audio trigger circuit has been updated for better low signal reliability
  • Master AC “vacation” switch on the rear panel

Power Output – Stereo Mode

  • 300 watts x 2, 8Ω both channels driven
  • 500 watts x 2, 4Ω both channels driven

Power Output – Bridged Mode

  • 1000 watts x 1, 8Ω
  • Bridged 4 Ω operation is not recommended
  • Power measurement are at 120 VAC: 0.1% THD, RMS continuous power, full audio band (20 Hz - 20 kHz)

Current Capacity

  • 60 amps peak, per channel

Slew Rate

  • > 130 volts per microsecond

Frequency Response

  • 5Hz - 100kHz, +0/-3dB 20Hz - 20kHz, +0/-0.25dB

Total Harmonic Distortion (THD)

  • < 0.1% at full power
  • < 0.03% at typical listening levels

IM Distortion

  • < 0.04%


  • Unmeasurable

Interchannel Crosstalk

  • > 80dB at 1kHz
  • > 70dB at 20kHz

Input Impedance

  • Unbalanced: 33kΩ
  • Balanced: 66kΩ,(33kΩ per leg)

Total Gain

  • 29dB

Input Sensitivity for 28.28V Output into 8 Ω

  • Unbalanced: 1 V
  • Balanced: 1V per leg

S/N Ratio

  • > 115dB, input shorted, IHF A-weighted
  • > 110dB, input shorted, unweighted

Damping Factor

  • > 1100 at 20 Hz

Power Requirement

  • Standby: 1 Watt
  • Idle (no music playing): 160 Watts
  • Typical Listening levels: 300 Watts
  • Maximum: 1400 Watts


  • Width: 17-5/8"
  • Height without feet: 7-1/8"
  • Height with feet: 7-3/4"
  • Depth: 20"
  • Depth with cables: 21-1/2"
  • Weight: 71 lbs.